Can't find a few parts for a portable RPI build

So I’m something of a noob when it comes to all this DIY stuff. I’ve worked with computers all my life, but never on such a level as to be essentially building the whole system by myself. So far, I’ve got most of what I need: a Raspberry Pi 2, the official 7" touchscreen, a mini wireless keyboard/mouse, a WiFi dongle, and a massive battery pack. As it is, everything’s up and running. But before I can call it finished and build the case, there are a couple of elements still remaining that I’m not entirely sure where to find them or even what to search in order to find them.

For one, I need a speaker I can mount inside the case once it’s built. This wouldn’t normally be hard to find, but in particular I’m hoping to find a way to set the speaker up so that I can easily switch between internal sound and a headphone jack. I was thinking of cheaping it out by trying to find some sort of switching audio splitter, but I can’t even find such a thing so I have no idea if it even exists. I’m assuming then that I’m probably going to have to come up with something myself, but being no expert on circuitry by any means, I could really use some help devising something.

The other major thing I have to come up with is a power switch. Again, I’m thinking I’m going to have to custom make something to get exactly what I want out of this. In particular, I’m looking to be able to easily switch between using the internal battery and an external power cable without having to disassemble anything. As for the switch itself, I’m not looking for anything fancy; I saw a tutorial on how to build a safe shutdown switch, for example, but I don’t intend on using a switch for that… I just want to be able to turn off power from the battery or wall.

If anyone can help me out here, I’d greatly appreciate it as I’m getting antsy and really want to get this build finished.